Forced flow steam generator and control therefor



FORCED FLOW STEAM GENERATOR AND CONTROL THEREFOR Filed March 10. 1959 P. PROFOS Nov. 6, 1962 5 shee tsheet 1 NOV. 6, 1962 PRQFQs 3,062,196

FORCED FLOW STEAM GENERATOR AND CONTROL THEREFOR Filed March 10. 1959 5 Sheets-Sheet 2 Nov. 6, 1962 P. PROFOS 3,062,196

FORCED FLOW STEAM GENERATOR AND CONTROL THEREFOR Filed March 10. 1959 5 Sheets-Sheet 3 lm emorz' P40 Bin/=0:

' ,By M

Nov. 6, 1962 P. PROFOS 3,062,196

FORCED FLOW STEAM GENERATOR AND CONTROL THEREFOR Filed March 10, 1959 5 Sheets-Sheet 4 I 730 I 730a lib ET 11a 7 720 127 5 720 127 l E I I lm emorz' IDAUI. Beams ,By Kl P, PROFOS Nov. 6, 1962 FORCED FLOW STEAM GENERATOR AND CONTROL THEREFOR Filed March 10, 1959 5 Sheets-Sheet 5 3,062,196 Patented Nov. 6, 1962 dice 3,062,196 FGRQED FLIBW STEAM GENERATQR ANE CGNTROL THEREFOR Paul Profos, Winterthur, Switzerland, assignor to Sulzer Freres, A., Winterthnr, Switzerland, a corporation of Switzeriand Filed Mar. 19, E59, Ser. No. 798,493

Ciaims priority, application Switzerland Mar. 10, 1953 9 tiiairns. (Ci. 122-479) The present invention relates to a forced flow steam generator in which the operating medium is divided into at least two streams, each stream passing through a tube system, whereby the tube systems are jointly heated by a combustion apparatus. This division of the steam generating system is particularly useful in large steam generators, because, otherwise, it is difficult to equally distribute the necessary heat to the great number of tubes of very large heating units through which tubes the operating medium flows in parallel relation.

It has been proposed to control the outlet temperatures of the individual streams of operating medium flowing through the individual tube systems of a steam generator by injecting water into the tube systems and to control the total amounts of feed water supplied to the systems according to the water injected into the respective systems. This method does not remove the causes of unequal heat distribution and corrects only the effect of the unequal heat distribution. For this reason it may happen that a steam generator is not fully loaded in all its parts, for example, if the fire favors one side of the steam generator. In that case the operation of the steam generator is not dependable and some tubes may be excessively heated.

It is an object of the present invention to provide a forced flow steam generator which avoids the aforesaid difiiculties. The steam generator according to the invention has a single, unitary combustion chamber and at least two separate tube systems placed in said combustion chamber through each of which tube systems an independent stream of operating medium is conducted, a control system being provided for distributing the fire so that all tube systems receive heat corresponding to the amounts of operating medium flowing through the systerns.

A steam generator according to the invention can be fully loaded in all its parts. Its operating dependability is much improved and control is much facilitated because the number of control operations necessitated by unequal heat reception is considerably lessened.

The control system according to the invention preferably includes means for measuring an operating characteristic which corresponds to the amount of operating medium passing through or to the heat reception of the individual tube systems, which means produce control signals afiecting the spatial distribution of the heat produced in a combustion chamber. As operating characteristics for the aforesaid control may serve, for example, the amount of water injected per time unit into the individual tube systems for controlling the outlet temperature thereof or the amounts of heat absorbed, per time unit, by the tube system.

The control signals described above may act on a comparing device producing signals corresponding to the difference between the control signals and used for actuating a device for distributing the heat produced in the combustion chamber to the individual tube systems. Means may be provided for equally distributing the total amount of feedwater into the individual tube systems.

Tilting burners may be used for distributing the heat to the individual tube systems according to the control signals. Alternatively, firing devices may be individually associated with the tube systems, if desired, in addition to a main combustion apparatus whereby the firing devices are actuated by the control signals. As a further modification the control system may regulate the amount of fuel supplied to individual firing devices according to the control signals.

The novel features which are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, and additional objects and advantages thereof will best be understood from the following description of embodiments thereof when read in connection with the accompanying drawing, in which:

FIG. 1 is a diagrammatic illustration of a steam generator and a control system therefor according to the invention and of a power plant connected thereto.

FIG. 2 is a diagrammatic illustration of an embodiment of the control apparatus forming part of the steam generator shown in FIG. 1.

FIG. 3 is a diagrammatic cross sectional view of a combustion chamber, tubular heating systems and firing apparatus according to the invention.

FIG. 4 is a diagrammatic cross sectional view of a combustion chamber and modified combustion apparatus according to the invention.

- FIG. 5 is a diagrammatic illustration of a fuel supply control system for the combustion apparatus shown in FIG. 4.

FIG. 6 is a diagrammatic illustration of a steam generator and modified control system therefor.

FIG. 7 is a diagrammatic illustration of another modification of a steam generator control system.

Referring more particularly to FIG. 1 of the drawing, numeral 11 designates a combustion chamber serving two tube systems I and II. Feedwater is supplied to the system I from a conduit 12 through a feed pump 13 and a feed valve 14. The latter controls the supply of feedwater to an economizer I5 wherefrom the water flows consecutively through an evaporator 16 into a preliminary superheater 17 and thereupon into a final superheater 18. The live steam leaving the superheater 18 drives a turbine 19 operating an electri generator 26.

The feedwater regulating valve 14 is controlled either in response to the temperature or to the pressure of the operating medium; in the illustrated example a thermostat 21 connected to the steam pipe interconnecting the super-heaters l7 and 18 produces a signal actuating a motor operator 22 which operates the valve 14. The temperature of the steam leaving the final superheater 18 is regulated by water injection in the conventional manner. A temperature sensing device 23 measures the steam temperature at the outlet of the superheater 18 and produces a signal which is conducted through a conductor 24 to a motor operator 25 for a valve 27 inter- 0 posed in a pipe 26 through which water suitable for injection is supplied from the conduit 12.

The tube system II corresponds to the system I. The individual parts of the tube system II are designated by the same numerals as are the corresponding parts in the system I whereby the numerals in system H are differentiated from those in the system I by the letter a. The two tube systems may have like or different dimensions. In the latter case the size of a turbine 19a receiving steam from the tube system 11 is different from that of the turbine 19.

The combustion apparatus includes a tilting burner 28 whose position relatively to the tube systems I and II can be changed by means of a motor operator 30 with which the burner is connected by a suitable mechanism 29.

Speed governors 31 and 31a respond to the speed of the shafts of the turbines I? and 19a, respectively, and

regulate the steam supply to the turbines in the conventional manner. The speed governors 31 and 31a are also connected by means of conventional conductors 32 and 32a to a controlling device 33 and, by means of conductors 34 and 34a, to a controlling device 35. The device 33 produces control signals passed through a conductor 36 to the motor operator 30 for the tilting burner 28. The device 35 produces control signals which are conducted through a conduit 37 to a motor operator 38 actuating a fuel control valve 39 in a fuel pipe 4% which supplies, for example, a liquid fuel to the burner 23.

FIG. 2 is a diagrammatic illustration of an example of a mechanism for controlling the position of the burner 28 and the fuel control valve 39. The sleeves of the speed governors 31 and 31a actuate levers 41 and 41a, respectively. A rod 43 is pivoted to the free end of the lever 41 and a link 44 is pivoted to the free end of the lever 41a. The lower ends of the elements 43 and 44 are pivoted to the ends of a two-arm lever 45. One end of a link 46 is pivoted to the center A of the lever 45. The other end of the link 46 is pivoted to the right end of a lever 46a which is linked to a pilot valve 47 of a hydraulic motor operator 38 actuating the fuel control valve 39 (FIG. 1). Downward movement of the valve 47 effects admission of a pressure fluid from a supply conduit 49 to a pipe 50 and to a chamber below a piston 51 forming part of the motor operator 38, moving the piston 51 upward. The pressure fluid above the piston 51 is simultaneously permitted to escape through a conduit 52. Upward movement of the piston 51 causes closing of the valve 39.

In order to provide the control apparatus with a proportional integral characteristic, the lever 46a has an arm 46b whose end is pivoted to a piston rod connected to the piston 51 and extending through a dashpot device 46d. A spring 460 connects the piston rod to a stationary part. The elements 46b, 46c and 46d form a yielding feedback. The part 43 to 46d form the controlling device 35 generally shown in FIG. 1.

A link 53 is pivoted to the lever 41a at the same distance from the stationary fulcrum 42a as the connection with the rod 44. The upper end of the link 53 is pivotally connected through a lever 54 to the upper end of the rod 43. The movement of the lever 54 is transmitted by a linkage 55, 56 to a pilot valve 57 of a hydraulic motor operator 30 for actuating the tilting burner 28. Upon downward movement of the pilot valve 57 a pressure fluid flows from a supply pipe 58 through the valve 57 and a conduit 59 into the space below a piston 66 forming part of the motor operator 30. This causes the piston 60 to move upward and to swing the burner 28 in clockwise direction (arrow 61). Upon upward movement of the pilot valve 57 a pressure fluid is admitted to the space above the piston 60 through a conduit 62, urging the piston 60 downward for moving the tilting burner 28 in counterclockwise direction (arrow 63). The pilot valve 57 is connected through a feedback lever 56a to the rod of the piston 60. The parts 43, 53 to 57 form the control device 33 generally shown in FIG. 1.

In the mechanism shown in FIG. 2 the pivot A of the lever 45 and therewith the pilot valve 47 are moved up or down according to the algebraic total of the deviations of the speeds measured by the governors 31 and 31a from the desired speeds. The pivot B of the lever 54 and therewith the pilot valve 57 are displaced according to the difference of the deviation of the speeds of the turbines 19 and 19a from the normal speeds. The described and illustrated control apparatus causes increase of the fuel supply to the burner 28 upon simultaneous reduction of the speeds of the two turbines 19 and 19a and vice versa, whereas if the speed deviations of the turbines are in opposite direction and of equal value the fuel supply is not changed.

In addition, the control apparatus has the following effect on the tilting burner 28. It is assumed that the speed of the turbine 19a has dropped below the desired speed because of insufiicient steam supply whereas the speed of the turbine 19 is above the desired speed. In this case the pilot valve 57 is moved downward whereby the piston 60 is moved upward according to the sum of the two speed deviations and the tilting burner 28 is swung in clockwise direction (arrow 61). This causes an increase of the heat supply to the tube system 11 and of the amount of steam produced thereby whereas the heat supply to the system I and the amount of steam supplied thereby are reduced. This returns the shafts speeds of the turbines to the desired values. The heat absorbed by the individual tube systems corresponds to the amounts of operating medium flowing through the tube systems. The correct amount of heat to the individual systems is assured by the position of the tilting burner 28 because this position depends on the speeds of the turbines 19 and 19a which speeds correspond to the amountsof heat absorbed by the respective tube systems.

The amount of steam produced by the individual tube systems may be changed because the firing of the tube systems is not uniform or the supply of operating medium is reduced, for example, because of scale deposition in the tubes. Ununiform heating may also be the result of soot deposition on the heating surfaces.

The .tube systems I and II individually consist of a plurality of tubes which are preferably arranged in groups of tubes which are in parallel relation with respect to the flow of the operating medium. The tube systems may be of the same or of different size. if they are of different size and the feedwater supply is distributed accordingly to the two tube systems, it is recommended to change the leverage of the levers 45 and 54 which is determined by the position of the pivots A and B and which determines the transmission of the movement of the sleeves of the governors 31 and 31a.

Combustion chambers of steam generators with which the present invention is concerned usually have a plurality of firing devices. FIG. 3 is a cross section through a combustion chamber 71 having a substantially quadratic configuration. Burners 72 and '75 are arranged in the corners of the combustion chamber. Tubes 76 lining two walls of the combustion chamber form a first tube system and tubes 77 lining the other two walls of the combustion chamber form a second tube system. Heating of the individual combustion chamber walls can be changed by tilting the burners 73 and 75. If the burners 73 and 75 are swung in the direction of the arrows 68, the tube system 77 will receive more heat. Swinging of the burners can be efiected, for example, by means of an apparatus as shown in FIGS. 1 and 2. The burners may also be arranged for swinging in a vertical plane.

The arrangement of the heating tubes in the combustion chamber shown in FIG. 4 is the same as in the combustion chamber shown in FIG. 3. In addition to the burners 72 and 75 which are located in the corners of the combustion chamber additional or auxiliary burners 78 to 31 are provided in the side walls of the combustion chamber. These auxiliary burners are supplied with fuel through pipes 82 to 85, respectively, in which regulating valves 86 to 89, respectively, are arranged. In the illustrated position the tube system 77 receives more heat than the tube system 76.

FIG. 5 is a diagrammatic illustration of an apparatus for controlling firing of the combustion chamber shown in FIG. 4, more particularly for controlling the amount of fuel supplied to the auxiliary burners. Electric motors operating the fuel supply valves 86 and 87 are supplied with electric energy through conductors 9t} and 91. The electric motors operating the fuel supply control valves 88 and 89 are connected to conductors 92 and 93. The conductors 9t) and 92 are connected to the center of resistors 94 and 95, respectively. The conductors 91 and 93 are connected to sliding arms 96 and 97, respectively, which slide on the resistors 94 and 95, respectively. The terminals of the resistors 94 and 95 are connected to a source of D.-C. current so that the current flows in opposite directions through the resistors. The wiper arms 96 and 97 are mechanically connected by a rod 98. Movement of the latter in the direction of the arrow 99 effects opening of the valves 86 and 87 and simultaneous closing of the valves 88 and 89 and vice versa. The arrangement may be so, that, if wipers 96 and 97 are in one extreme position, the respective valves are fully closed and the other valves fully opened. The rod 98 is connected to a piston 18% of a hydraulic servo-motor 101 which may be connected, for example, to the pressure fluid conduits 62 and 59 shown in FIG. 2.

The steam generator schematically illustrated in PEG. 6 has two tube systems Ill and IV, each including an economizer 1111, 111a, respectively, evaporator 112, 112a, respectively, superheater 113, 113a and final superheater 114, 114a, respectively. Preheated feedwater is pumped into a pipe 116 by a feed pump and divided into two pipes 117 and 118. The latter are provided with measuring orifices 1 19, 120, respectively. The pressures measured downstream of the orifices are transferred through conduits 121, 122, respectively, to spaces above and below a diaphragm 123 of a pressure difference measuring device 124. The diaphragm acts in the conventional man ner on a pilot valve 125 of a hydraulic motor operator 126 whose piston is connected to a valve 127 in the pipe 118 for actuating the valve. A valve 128 is interposed in the pipe 117. This valve may be operated, for example, by conventional means, not shown, in response to the steam temperature downstream of the evaporator 112. The described apparatus equally distributes the feedwater into the tube systems III and IV by opening or closing the valve 127 according to the pressures measured by the device 124 which pressures are different, if the amounts of water flowing to the systems III and IV are different.

Pipes 129 and 129a are connected to the feed pipe 116 for conducting water through valves 13a and 138a, respectively, to water injectors 131 and 131a which are located between the superheaters 113, 114 and 113a, 114a, respectively. The valves 138 and 1365a are controlled in the conventional manner according to the temperatures of the live steam leaving the steam generators and measured by thermostats 132, 132a, respectively, which control motor operators for valves and 138a.

A tilting burner 134 is placed in a combustion chamher 1333, serving the two tube systems. The burner receives fuel through a conduit 135 and a valve 136 which is controlled, for example, in the same manner as the valve 39 in the system shown in FIG. 2.

Since the feedwater is equally distributed into the two tube systems a difference of the heating of the tube systems Ill and IV causes a ditference in the amounts of water injected into the two tube systems for maintaining the desired live steam temperatures. It also causes a difference in the amounts of steam produced by the individual systems. In the example illustrated in FIG. 6 the amounts of injected water are made responsible for the control of the heat distribution to the tube systems.

Measuring orifices 1 :8- and 149a are provided in the water injection pipes 129, 129a, respectively. The pressures of the injection water downstream of the orifices act through conductors 141, 141a on a pressure difference meter 142 including a diaphragm 143. The latter is connected to a pilot valve 144 receiving a pressure fiuid from a supply pipe 145. Downward movement of the pilot valve 144 permits flow of pressure fluid through a conduit 146 to the space below a piston 147 forming part of a motor operator 143 and being connected by a linkage 149 to the tilting burner 134. Increase of pressure below the piston 147 causes an upward movement of the piston and swinging of the burner 134 in the direction of the arrow 150; upward movement of the pilot valve 144 causes swinging of the burner in the opposite direction (arrow 151).

With the apparatus shown in FIG. 6 the tilting burner is moved toward the tube system which receives less injection water than the other tube system.

The embodiment of the invention illustrated in FIG. 7 is suitable for a subcritical pressure steam generator. The feedwater supplied by a feed pump 161 is divided into two parts which flow in tube systems V and VI, consecutively through economizers 162, 162a, respectively, evaporators 163, 163a, respectively, superheaters 164 and 164a, respectively, and finally superheaters 165, 165a. The generated steam is conducted through a live steam pipe 166 to consumers, not shown. Each tube system includes a water separator 167, 167a, respectively, which are interposed between the evaporators and the first superheaters where there are only a few percents moisture in the operating medium so that substantially dry steam flows into the superheaters.

The water separators 167 and 167a are provided with conventional water level controls which are alike for both separators and of which only the one is shown which is connected to the separator 167a.

Cooling water can be injected into each tube system through pipes 168 and 168a according to the temperatures measured by temperature sensing devices 169' and 169a which measure the temperatures of the superheated live steam leaving the tube systems and which actuate cooling water control valves 170 and 173a, respectively.

The control system shown in FIG. 7 is actuated according to values corresponding to the amounts of heat ab- Sorbed by the individual tube systems. For this purpose the sum of heat is measured which is contained in the live steam produced by the systems and in the blowdown water removed from the water separators. The blowdown pipe 171 of the system V is provided with a temperature measuring device 172 and a flow meter 174- including an orifice plate 173. A device 175 forms the product of the temperature 1 measured by the device 172 and of the amount Q of blowdown water measured by the device 173, 174 and produces a signal corresponding to the amount of heat removed with the blowdown water. This signal is transmitted through a conductor 167 to a summing device 177. A signal corresponding to the amount of heat removed with the live steam is produced by a device 178 and conducted through a conductor 179 to the summing device 177. The amount of superheated live steam produced by the tube system V is measured by means of a flowmeter including an orifice plate 188- and a corresponding signal is conducted into the device 178. The temperature of the superheated live steam is measured by the device 169 and a corresponding signal is conducted into the device 178.

The tube system VI is provided with corresponding apparatuses for measuring the amount of heat removed with the blowdown water from the separator 167a and with the superheated live steam leaving the system VI.

Conductors 181 and 181a connect the summing devices 177 and 177a to a comparing device 182 which produces a signal corresponding to the difference of the sums formed in the devices 177 and 177a which signal is transmitted through a conductor 183 to a motor operator 184 for rocking a tilting burner 185. The control apparatus is so constructed that the tilting burner is directed towards the tube system from which a lesser total amount of heat is removed. The comparison device 182 may be constructed as shown in the example shown in FIG. 2. If desired, the control may be made more accurate by introducing a signal into the device 182 which corresponds to the load. For this purpose a flow signal may be produced by means of an orifice plate 186 interposed in the steam main 166 and transmitted through a conductor 187 to the device 182 wherein the energy of the signal produced by the device 182 is increased upon a decrease of the load and vice versa.

The invention is not limited to the illustrated and described examples. It can be used in steam generators having more than two tube systems which are all associated with the same combustion chamber. If desired, one or more of the tube systems may be used as controlling systems whereby the heat supplied to the other systems is controlled according to the demands of the controlling tube systems. It is also possible to combine heating surface portions of several tube systems. For example, the total amount of feedwater may be conducted through a single economizer and thereupon distributed into different tube systems. The invention can be applied to steam generators operated at subcritical as well as critical or at supercritical pressure of the operating medium. In a forced flow critical pressure or supercritical pressure steam generator the evaporators 16, 16a in FIG. 1 and 112, 112a in FIG. 6 are, in fact, no evaporators because there is no coexistence of the liquid and the steam phase. There is a transition zone in these parts of the tube systems where the liquid phase immediately changes into the steam phase.

Instead of the tilting burners other means may be provided for directing the hot gases to selected heating Surfaces. The hot gases produced by a stationary combustion apparatus may be directed toward a selected heating surface by suitable arrangement of the supply of primary and/or secondary combustion air.

I claim:

1. A steam generator comprising a single, unitary combustion chamber, at least two separate substantially identical tube systems placed in said combustion chamber and conducting an operating fluid in two parallel streams, each of said tube systems comprising a water heating section, an evaporating section, and a superheater section, said sections being arranged in series relation with respect to the flow of Water and steam therethrough, a firing apparatus in said combustion chamber, said firing apparatus including control means for altering the relative heating effect of said firing apparatus on the individual tube systems, and control signal producing means responsive to values individually corresponding to the heat absorption by the fluids in the separate tube systems and being operatively connected to said control means for actuating the latter for decreasing the heating efiect of said firing apparatus on a first of said tube systems and for simultaneouly increasing the heating eiTect of said firing apparatus on a second of said tube systems, upon an increase of the vdue corresponding to the heat absorption by said first tube system relative to the value corresponding to the heat absorption by the second tube system, and vice versa.

2. A steam generator as defined in claim 1 wherein said control signal producing means are responsive to the amounts of operating fluid flowing through the individual tube systems and operatively connected to said control means for actuating the latter for altering the relative heating effect of said firing apparatus on said tube systems according to the amounts of operating fluid flowing through the individual tube systems whereby the heating efiect on a first of said tube systems relatively to the heating effect on a second of said tube systems is increased if the amount of operating fluid flowing through the first tube system increases relatively to the amount of operating fluid flowing through the second system, and vice versa.

3. A steam generator as defined in claim 1, wherein said firing apparatus includes at least one tilting burner, said control means being connected to said tilting burner for controlling the position of said burner in response to said values.

4. A steam generator as defined in claim 1, wherein said firing apparatus includes regulating means for regulating the supply of fuel to said firing apparatus, means responsive to a value corresponding to the total amount of heat absorbed by said tube systems being operatively connected to said tube systems and to said regulating means for increasing the fuel supply upon a decrease of the total amount of heat absorbed by said tube systems below a preset value and vice versa.

5. A steam generator as defined in claim 1 including, in combination with said firing apparatus, a main combustion apparatus in said combustion chamber for producing heat for heating said tube systems.

6. A steam generator as defined in claim 1, wherein said firing apparatus includes at least two individual combustion devices individually associated with said tube systems for supplying heat thereto, said control means including fuel supply regulating means operatively connected to said combustion devices for regulating the relative fuel supply to said combustion devices.

7. A steam generator comprising at least two separate tube systems through which the operating medium flows in two parallel streams, a unitary combustion chamber common to both tube systems, a firing apparatus in said combustion chamber, said firing apparatus including heat energy distributing means for controlling the distribution of the heat produced by said firing apparatus to said tube systems, and a control system including measuring means operatively connected to each of said tube systems and individually measuring a value characteristic of the operation of the respective tube system, a control signal producing means connected to both of said measuring means and being responsive to the difference of the values measured by said measuring means for producing control signals corresponding to said difference, said control signal producing means being operatively connected to said heat energy distributing means for distributing the heat produced by said firing apparatus to said tube systems according to said difference whereby the heat supply to a first of said tube systems is increased and the heat supply to a second of said tube systems is decreased to a degree corresponding to said difference of said values.

8. A steam generator comprising at least two individual tube systems through which the operating medium flows in two parallel streams, a combustion chamber common to both tube systems, a firing apparatus in said combustion chamber, said firing apparatus including heat energy distributing means for controlling the distribution of the heat produced by said firing apparatus to said tube systems, water injecting means individually connected to said tube systems for injecting cooling water thereinto, temperature measuring means individually connected to said tube systems downstream of the connection of said water injecting means for measuring the temperature of the operating medium thereat, controlling means connected to said temperature measuring means and to said water injecting means for controlling the amount of water injected into the individual tube systems for maintaining the temperatures of the operating medium in the individual tube systems downstream of the connection of said water injecting means at a predetermined value, operating medium flow control means connected to the inlet of the individual tube systems for equalizing the amounts of operating medium flowing through the individual tube systems, and a control system including measuring means operatively connected to said water injecting means for measuring the flow of cooling water to the individual tube systems, control signal producing means connected to said cooling water flow measuring means and being responsive to the difierence of the flow of cooling water to the individual tube systems, said control signal producing means being operatively connected to said heat energy distributing means for distributing the heat produced by said firing apparatus to said tube systems according to said difierence whereby, upon a decrease of the cooling water flow to one of said tube systems, the heat supply to the respective tube system is increased and the heat supply to the second of said tube systems is decreased.

9. A steam generator comprising at least two individual tube systems through which the operating medium flows in two parallel streams, a combustion chamber common to both tube systems, a firing apparatus in said combus-' tion chamber, said firing apparatus including heat energy distributing means for controlling the distribution of the heat produced by said firing apparatus to said tube systems, water injecting means individually connected to said tube systems for injecting cooling water thereinto, temperature measuring means individually connected to said tube systems downstream of the connection of said water injecting means for measuring the temperature of the operating medium thereat, controlling means connected to said temperature measuring means and to said water injecting means for controlling the amount of water injected into the individual tube systems for maintaining the temperatures of the operating medium in the individual tube systems downstream of the connection of said water injecting means at a predetermined value, and a control system including measuring means operatively connected to said water injecting means for measuring the flow of cooling Water to the individual tube systems, control signal producing means connected to said cooling water flow measuring means and being 10 responsive to the difference of the flow of cooling water to the individual tube systems, said control signal producing means being operatively connected to said heat energy distributing means for distributing the heat produced by said firing apparatus to said tube systems according to said difference whereby, upon a decrease of the cooling Water flow to one of said tube systems, the heat supply to the respective tube system is increased and the heat supply to the second of said tube systems is de- 10 creased.

References Cited in the file of this patent UNITED STATES PATENTS 2,590,712 Lacerenza Mar. 25, 1952 15 2,695,599 Armacost Nov. 30, 1954 2,752,899 Kasak July 3, 1956 FOREIGN PATENTS 758,833 Great Britain Oct. 1-0, 1956 

